Resinous compositions and fire-resistant laminates prepared therefrom



*RESINOUSCOMPOSITIONS AND FIRE-RESISTANT "LA-MINATES PREPARED THEREFROM'-David E.:Baldwin, Hampton, S. C., and RobertH. Runk, Jittsburgh, -Pa.,assignors to Westinghouse Electric .Corporation, East Pittsburgh, Pa., acorporation of Pennsylvania fNo Drawing. Application. July: 15, 19,54,Serial No. 443,720

v 9 Claims. (Cl. 154-2.6)

'-t-ion, as well as high strength and other physical properties.Resinous laminates of this type in the forms of plates, tubes, channels,angles and other forms are particularly 'desirable for use inswitchgear, switchboards, tap changers and similar'electrical apparatusthat may be subjected to electrical arcs due to opening of. electricalcontacts' The art has produced a considerable number of laminateswherein expedients, such as incorporation of "fireproofing agents, havebeenmade use of. In most cases, however, these added fireproofingagents, such for example as chlorinated materials, have reduced thestrength of the laminates or the electricalresistance properties, andconsequently, satisfactory results have not been obtained. Certainfire-resistant resins, such as melamine formaldehyde resins,--arenotonly substantially more expensiyejthanphenolic resins, but when appliedto cellulosic fibrousmaterials, their moisture resistance is poor. Thedielectric strength of melamines is not as high as vthat of othercheaper laminates, and thick sections, that is overone-quarter of aninch, tend to crack badly on :aging, particularly at temperatures of 100C. For examplega melamine formaldehyde laminatell z inches thick whenheated to 100 C. had cracked badly in one :day.

In testing the-fire resistance of laminates, we have em- ..ployeda testthatis a slight modification, as advocated by Gale, Stewart and Alfers,in the ASTM Bulletin, page 23, December 1944, of Method 2023.1 ofFederal Speci- 'fication LP-406b. The test equipment comprises aventilated'box approximately l8inches square in cross section and about3 feet high with an opening at the top .in which there is disposed aconstant speed exhaust fan to withdrawgases 'from the box. At the:bottom of the box is located a four-jawed chuck adapted to hold in avertical position laminate specimens having dimensions of /2 inch 'bycinch-by 5 inches in length. A heating coil composed of nickel-chromiumalloy wound on a 1 .inch diameter of a length of Z'inchesgis locatedwith its center. about the specimen held-in the chuck. Above thetop.turn of this heating coil are disposed two automobile spark plugswith their ignition-electrode tips approximately of an inch away fromtwo opposite sides of ,the laminatesample'tobe tested.

:In testing a sample of the laminate, a rod of the .sample machined todimensions of /2 inch by /2 inch by 5 inches in length is insertedin-thechuck, andtheheat- .ingcoil iszenergized with 55 amperes of electricalcur- .rent and the spark plugs are energized with electrical cur-.rentso that an electrical .arc plays .across .the ignition electrodescontinuously. The ignition time is the United States Patent 0 elapsedtime from the start of energization of the coil and the arcing of thespark plugs until a flame settles upon the sample. Once a flame appearsabout the sample, the flow of electrical current to the spark plugs isterminated, but the heating coil is energized for 30 seconds longer atwhich time electrical current to the coil is also turned off and timingis begun from the moment that current to the coil is terminated untilthe flame extinguishes, this latter time period being designated as theburning time of the sample. It will be apparent that both the ignitiontime and burning time are factors of considerable value in selectingfire resistant laminates.

The object of this invention is to provide for thermosettable resinousreaction products comprising phenol, dicyandiamide and formaldehyde,which when applied to fibrous sheet material and cured under heat andpressure result in resinous laminates that are highly fire resistant.

A further object of the invention is to provide thermoset laminatescomprising a fibrous sheet material and a .thermoset reaction product ofphenol, dicyandiamide and formaldehyde, which laminate has a high fireresistance, good electrical insulating properties and high physicalstrength.

Other objects of the invention will, in part, be obvious and will, inpart, appear hereinafter.

We have discovered that highly fire-resistant thermoset resinouslaminates may be prepared from a resinous prodnot derived by reactingphenol, dicyanidiamide and formaldehyde in the proportions of 1 mole ofthe phenol, from 0.8 to 2 moles of dicyandiamide and from.0.9 to 1.5moles of formaldehydelper mole. of the phenol and. dicyandiamide. Wateris present, being usually furnished as a part of aqueous formaldehydesolution (37% .to 40%.), and amounting to at leastv 10% of the weight ofthe reactants, and ordinarily should not exceed the weight of thereactants. The mixture is reactedunder alkaline conditions for at least/2 hour, and preferably by refluxing from 1 to 2 hours, and then isvacuum dehydrated at a temperature not exceeding C. until substantiallyall of the water is removed and then a volatile solvent is applied toproduce an impregnating varnish.

Tie varnish may include a small proportion of the order of 2% to 10% byweight of finely divided solids such assilica, aluminum oxide, antimonyoxide and the like refrac-torysolids to impart better flame resistance.

The-impregnating varnish'is applied tofibrous sheet materialsandparticularly cellulosic fibrous materials,- such as kraft paper,alpha paper and cotton cloth. Exceptional flame resistant properties andhigh strengths are obtained using such cellulosic materials. However,other fibrous materials may be used, such as glass cloth, glass mat,

asbestos cloth, nylon cloth and other synthetic resinous fibrousmaterialispassed through an oven or other dryer after each dipto remove thevolatile .solvent. During drying, it is desirable to heat the fibrousmaterial treated with the varnish composition at a temperature of fromC. to C. in order to remove the solvent therefrom promptly and toadvance the cure of the resin well into the B stage. The heat treatmentof the applied phenol-.dicyandiamide-formaldehyde resin at this stage isconducted so that the resulting treated fabric has a green ness offrom0.5 to 10%. The greenness is determined byplacing a small piece ofthe-resin treated sheet mate- .rial in-aIhot-press at atemperature of C.and a pressure of 1,000 pounds per square inch for 5 minutes, .and thenmeasuring the amount of resin that'is forced out or by employingwater-alcohol mixtures as the solvent.

the sample, that is, the resin that extends beyond the fibrous sheetmaterial proper, and determining the pro portion of this exuded resin toall of the resin in the sample. A greenness of is relatively high and isdesirable for the making of certain products, such as tubes whichrequire a considerable flow of resin between laminations in order thatthe laminations bond adequately. A greenness of about 0.5% on the otherhand is relatively low but is essential for the purpose of making thickflat laminates, for example, V inch thickness and greater. For preparinglaminates of thicknesses of V8 inch, a greenness of from 1% to 3 isadequate.

The sheet fibrous material, with the applied B stagephenol-dicyandiamide-formaldehyde resinous product thereon, may bemolded into laminates, tubes and other members by superimposing aplurality of layers of the treated sheet material and compressing it atpressures of from 150 to 5,000 pounds per square inch at temperatures offrom 135 C. to 165 C. It will be appreciated that the fibrous sheetmaterial may be chopped or macerated, or otherwise treated, and membersmolded fromv such comminuted fibrous material. Of course, the higheststrength products are secured with laminates made from superimposedlayers of the impregnated fibrous sheet material.

In preparing the varnish impregnating composition from the resinousreaction product, we have secured particularly good results by using asa solvent a mixture of ethanol .may be employed, as desired. We haveobtained exceptionally well impregnated cellulosic sheet fibrousmaterial y employing mixtures containing 50% or more by weight of water,the balance being ethanol, we have secured particularly thoroughimpregnation of paper and cotton fabrics.

The following examples are illustrative of the practice of theinvention.

EXAMPLE I Into a steam heated reaction kettle there were introduced thefollowing:

Parts by weight Phenol 2750 Dicyandiamide 2100 Formaldehyde (37%) 4620Ammonia (28%) 166 The ammonia and the formaldehyde were admixed beforebeing introduced into the kettle with the remainder of the ingredients,the mixture having a pH of approximately 8.5. The mixture was slowlyheated, and at 80 C. an exothermic reaction took place that carried thetemperature to approximately 95 C. Additional heat was then supplied inorder to cause the reaction mixture to reflux. The mixture was refluxedfor 90 minutes and then dehydrated under a vacuum of 28 inches ofmercury, and the temperature gradually increased to approximately 75 C.during dehydration. Substantially all the water had been removed. To thehot reaction product there was added 2000 parts by weight of 95%ethanol, and the resulting thick varnish was cooled to room temperature.The resinous reaction product was then further diluted with a mixturecomprising 50% by weight of ethanol and 50% by weight of water toproduce a solution comprising approximately 53% by weight of resinsolids. The viscosity of the composition is approximately 250centipoises.

The resulting varnish of this Example I was employed to impregnate thefollowing sheet fibrous materials:

(1) 10 mil thick alpha paper, the impregnated paper containing 101% ofits weight of the resin solids at a greenness of 0.5%.

reaction 4 (2) 5 mil thick kratt paper, the treated paper contain- 1 ing98% of its weight of resin solids, the greenness being (3) 6 /2 ouncebleached cambric, the resin solids being equal to the weight of thecambric, the greenness being 0.5%.

Laminates were prepared from each of these three impregnated materialsby superimposing a sufficient number of laminations to produceconsolidated members of various thicknesses of up to V2 inch. Thesuperimposed layers were consolidated at 1,000 pounds per square inchwith the temperature of the press platens slowly rising to a finaltemperature of 165 C. The following table sets forth the ignition timeand burning time in seconds of the laminates, and includes a standardXXX-grade phenolic laminate prepared from alpha cellulose paper forcomparison purposes.

It will be apparent that the first three laminates are considerablysuperior in ignition time and very much better in burning time to thestandard XXX phenolic.

The dielectric properties of the laminates used in Table I were thendetermined, both in the as-received condition and after humidificationand water immersion, and these data are set forth in Table II.

TABLE II Dielectric properties 100 Tan 8 Dielectric Test ConstantLaminate Conditions 1 60 ey 1 Key lMey 60 cy 1 Key 1 Mcy A 1.09 1.442.19 4.89 4.78 4.51 Alpha-base... C96/23/96 4.55 4.12 4.28 6.22 5.864.90 D24/23 4.60 3.60 3.14 5.67 5.59 5.15 A 1.18 1.44 2.17 4.79 4.684.34 Krait-base C 6.47 4. 43 4.60 6.48 6.02 4.93 D 8.30 4.37 4.26 6.145.89 5.15 1.93 1.75 2.57 4.97 4.81 4.49 Cambric-base C96/23/96 14.6 6.195.23 6.45 5.63 4.64

a ii? it? 222 .16 4. 7 XXX P11910110 {13-24 23 14.3 6.7 6.18 6.80 5.804.32

1 OonditionA Tested as received.

OOHdllilOD. O-96/23/96 After 96 hours at 23 0. and 96% relativehumidity. Condition D-24/23" Tested after 24 hours immersion indistilled water at 23 C.

The physical properties of the laminates were also determined, and thesedata are set forth in Table III.

Laminates made from kraft paper treated with the resin of Example I to aresin content, exhibited tensile strengths of 22,800 p. s. i., flexuralstrength of 28,050 p. s. i., compressive strength of 51,320 p. s. i.,and izod impactof 2.2 ft. 1bs. per-inch width flatwise (XXX gradephenolic having an izodimpact of 1.4 ft. lbs. per inch .width flatwise)EXAMPLE II The procedureof Example I was employed in reacting the Jfollowing:

Phenol pounds 560 Dicyandiamide do 500 Formaldehyde (37%) do 1160'Ammonia (28 gallons 3 The mixture was dehydrated under a vacuum of 27inches of mercury and a final. temperature of 70 C. The resultingreactionproductwas then dissolved in a solvent mixture comprising90gallonsof 95% ethanol and 35 gallons of water. The resulting varnishhad a viscosity of approximately 250 centipoises and between 52% and .55by weight of recoverable resin solids. The set time 'goods are treatedwith solvents and the like to remove naturallypresent-waxes and thelike. However, we have employed 3 ounce grey cottonfabric which has notbeen treated toremove waxes and other naturally present impurities, andimpregnated the fabric with the varnish composition of this Example IIto provide thereon an amount of resin solids equal to the weight of thecotton fabric. The greenness of the fabric varied from 1 to 3% forditferent batches thereof. Laminates of a thickness of inch and inchwere molded from this treated cotton fabric employing, however, a topsheet of the same cotton fabric containing the resin in an amount equalto 150% of the weight of the fabric. Such laminates were consolidated ina hot press at 1,500 pounds per square inch at 155 C., and were testedfor their electrical properties. The water absorption of the ,4 inchlaminate after immersion in water for 2.4 hours at 25 C. was 1.05%,while the Vs inch laminate absorbed only 0.677%. Bleached cotton fabricmade into similar laminates absorbed 75% more water than did thegrey-goods base laminate of this example. The dielectric strength of thegrey goods laminates was 522 volts per mil thickness for the inchlaminate and 372 volts per mil thickness for the Ms inch laminate. Thesedielectric strength values are excellent and equal to those of the bestphenolic laminates available in the trade.

It will be understood that the resinous compositions of this inventionmay be prepared by substituting cresol for a part or all of the phenol.Furthermore, the phenol, dicyandiamide and formaldehyde may be reactedwith other alkali catalysts than ammonia, and in some cases, we havefound that the reaction will occur without the extraneous addition ofany catalysts whatever. Suitable alkali catalysts are sodium hydroxide,sodium carbonate, disodium phosphate, calcium oxide and barium oxide.The catalysts may be employed in an amount of up to based on the weightof the phenol.

The laminates of this invention have been applied with considerablesuccess to circuit interrupters. Thus, arc barriers, splitters, channelsand tubes and insulating supports for conductors, as well as the covers,bases and other structural parts not necessarily subject to full voltageof the conductors, have been prepared from the laminates of thisinvention. The laminates withstood arcs between contacts of such circuitinterrupters with no burning, or in exceptional cases, any flamesextinguished themselves promptly on termination of the arc. Fuse tubesand other fuse elements may be advantageously made from the laminates.Switchboards and cubicles containing electrical members subject toconsiderable .and arcing members.

6 heating. from red hot resistors and other over-heated conductorsand..occasional arcing, may be fabricated from the laminates of thisinvention to advantage. It will be apparent that we have producedlaminated members that can be used to great advantage with successfulflame retardation in the vicinity of-hot electrical conductors Jacketsfor bus bars are other insulating applications for the insulatingmembers of this invention. It will be appreciated that the resinousmembers may be employed for non-electrical uses, especially near flamesor hot objects.

.It will be understood thatthe above examples and description areillustrative and not in limitation of the invention.

We claim as our invention:

1. In the process of preparing fire-resistant thermoset resinouslaminates, the-steps comprising impregnating a sheet fibrous materialwith a solution of a thermosettable resinous product derived by reactingonlyone mole of a phenol, from 0.8 to 2.0 moles of dicyandiamide, and

from 0.9 to 1.5 moles of formaldehyde per mole of the phenol anddicyandiamide in the presence of water and an alkali catalyst in anmount of up to 5% of the weight .of the phenol, the mixture beingrefluxed for a least /2 hour and then vacuum dehydratedat a temperaturenot dissolved in a volatile solvent to provide the said impregnatingsolution, the resin impregnated sheet fibrous material being heated todrive off the solvent and to advance the cure-of the resin to acondition where its greenness is less than5%, the fibrous sheet carryingfrom 0.7 to 2 times its weight of the resin after drying, superimposinga plurality of layers of the resin treated fibrous sheet and molding thesuperimposed layers at a pressure of from 500 to 5,000 pounds per squareinch at temperatures of from 135 C. to 165 C. to fully cure the appliedresin and to produce a thermoset laminate.

2. The process of claim 1, wherein the resious product is derived fromthe mixture by including an alkaline catalyst.

3. The process of claim 1, wherein the volatile solvent comprises amixture of ethanol and Water in the proportions of from 20% to 80% byweight of ethanol.

4. The process of claim 1 wherein the sheet fibrous material comprisescellulose and the volatile solvent in a mixture of water and ethanol inthe proportions of from 20% to 80% by weight of ethanol.

5. An impregnating varnish comprising in combination (a) from 30% to 60%by weight of a thermosettable resinous product derived by reacting onlyone mole of a phenol, from 0.8 to 2.0 moles of dicyandiamide, and from0.9 to 1.5 moles of formaldehyde per mole of the phenol anddicyandiamide in the presence of water and an alkali catalyst in anamount of up to 5% of the weight of the phenol, the mixture beingrefluxed for at least /2 hour, and then vacuum dehydrated at atemperature not exceeding C., and (b) from 70% to 40% by Weight of avolatile solvent comprising amixture of ethanol and water, the ethanolcomprising from 20% to 80% by weight of the volatile solvent.

6. A fire-resistant thermoset laminate comprising a plurality of layersof sheet fibrous material and a thermoset resin impregnating each of thelayers, the thermoset resin also uniting the layers, the thermoset resincomprising from 0.7 to 2 times the weight of the sheet fibrous material,the thermoset resin comprising the cured resinous product derived byreacting only one mole of a phenol, from 0.8 to 2.0 moles ofdicyandiamide, and from 0.9 to 1.5 moles of formaldehyde per mole of thephenol and dicyandiamide in the presence of water and an alkali catalystin an amount of up to 5% of the weight of the phenol, the mixture beingrefluxed for at least /2 hour, and then vacuum dehydrated at atemperature not exceeding 100 C.

7. A fire-resistant thermoset laminate comprising a plurality of layersof cotton fabric and a thermoset resin uniting the layers, the thermosetresin comprising from 0.7 to 2 times the weight of the sheet fibrousmaterial, the thermoset resin comprising the cured resinous productderived by reacting only one mole of a phenol, from 0.8 to 2.0 moles ofdicyandiamide, and from 0.9 to 1.5 moles of'formaldehyde per mole of thephenol and dicyandiamide in the presence of water and an alkali catalystin an amount of up to 5% of the Weight of the phenol, the mixture beingrefluxed for at least /2 hour, and then vacuum dehydrated at atemperature not exceeding 100 C., the resulting resinous reactionproduct being dissolved in a mixture of water and ethanol, the solutionbeing applied to the cotton fabric and dried to evaporate the solventand to advance the reaction product to the B stage.

\ 8. In a circuit interrupter having an electrical conductor whereinarcing develops during operation of the circuit interrupter and subjectto high temperatures, an insulating member comprising a fire-resistantthermoset laminate comprising a plurality of layers of sheet fibrousmaterial and a thermoset resin uniting the layers, the

phenol, from 0.8 to 2.0 moles of dicyandiamide, and from 0.9 to 1.5moles of formaldehyde per mole of the phenol and dicyandiamide in thepresence of water and an alkali catalyst in an mount of up to 5% of theweight of the phenol, the mixture being refluxed for a least /2 hour,and thenvacuum dehydrated at a temperature not exceeding 100 C., saidmember having a high resistance to ignition and rapid extinguishing ofany flames.

9. In an electrical member having an electrical conductor subject to thedevelopment of high temperatures during operation, an insulating membercomprising a fire-resistant themoset laminate comprising a plurality oflayers of sheet fibrous material and a thermoset resin uniting thelayers, the thermoset resin uniting the layers, the thermoset resincomprising from 0.7 to 2 times the weight of the sheet fibrous material,the thermoset resin comprising the cured resinous product derived byreacting only one mole of a phenol, from 0.8 to 2.0 moles ofdicyandiamide, and from 0.9 to 1.5 moles of formaldehyde per mole of thephenol and dicyandiamide in the presence of water and an alkali catalystin an amount of up to 5% of the weight of the phenol, the mixture beingrefluxed for at least /2 hour, and then vacuum dehydrated at atemperature not exceeding 100 C., said insulating member having a highresistance to ignition due to the high temperatures and being rapidlyself-extinguishing.

References Cited in the file of this patent UNITED STATES PATENTS1,938,917 Loetscher Dec. 12, 1933 2,314,701 Harvey Mar. 23, 19432,315,400 DAlelio Mar. 30, 1943 2,328,825 McMahon Sept. 7, 19432,606,885 Schmutzler Aug. 12, 1952 2,660,215 Arone Nov. 24, 1953

1. IN THE PROCESS OF PREPARING FIRE-RESISTANT THEREMOSET RESINOUSLAMINATES, THE STEPS COMPRISING IMPREGNATING A SHEET FIBROUS METERICALWITH A SOLUTION OF A THERMOSETTABLE RESINOUS PRODUCT DERIVED BY REACTINGONLY ONE MOLE OF A PHENOL, FROM 0.8 TO 2.0 MOLES OF DICYANDIANMIDE, ANDFROM 0.9 TO 1.5 MOLES OF FORMALDEHYDE PRE MOLE OF THE PHENOL ANDDICYANDIANMIDE IN THE PRESENCE OF WATER AND AN ALKALI CATALYST IN ANAMOUNT OF UP TO 5% OF THE WEIGHT OF THE PHENOL, THE MIXTURE BEINGREFLUXED FOR AT LEAST 1/2 HOUR AND THEN VACUM DEHYDRATED AT ATEMPERATURE NOT EXCEEDING 100*C., THE RESULTING REACTION PRODUCT BEINGDISOLVED IN A VOLATILE SOLVENT TO PROVIDE THE SAID IMPREGNATINGSOLUTION, THE RESIN IMPREGNATED SHEET FIBROUS MATERIAL BEING HEATED TODRIVE OFF THE SOLVENT AND TO ADVANCE THE CURE OF THE RESIN TO ACONDITION WHERE ITS GREENNESS IN LESS THAN 5%, THE FIBROUS SHEET CRYINGFROM 0.7 TO 2 TIMES ITS WEIGHT OF THE RSIN AFTER DRYING, SUPERIMPOSING APLURALITY OF LAYERS OF THE RESIN TREATED FIBROUS SHEET AND MOLDING THESUPERIMPOSED LAYERS AT A PRESSURE OF FROM 500 TO 5,000 POUNDS PER SQUAREINCH AT TEMPERATURES OF FROM 135*C. TO 165*C. TO FULLY CURE THE APPLIEDRESIN AND TO PRODUCE A THERMOSET LAMINATE.